There is currently no toggle for it in the admin, but I will definitely suggest adding it to the base framework; and I'll add it to new WP releases until the overall framework has it.
If you really need to disable it, you can comment out (put "//" in front of it)
add_filter('widget_title', 's5_widget_h3_first', 11);
on line 32 of [themedir]/vertex/includes/wp_vars.php
That will disable the filter I made for WP to enable that function.